Fuel economy is an ever increasing consideration for vehicle owners, because fuel is one of the leading operating costs in owning a vehicle. In typical axle configurations, fuel economy savings are realized by altering the gear ratios. In such typical axle configurations, the axles are designed to have a single lubricant reservoir. The amount of lubricant required for any given axle is then set based upon the thermal limitations of the axle components. The maximum temperature goal is set by a worst case duty cycle of the axle, which generally requires a high volume of lubricant to achieve the thermal goals of the axle. This high volume of lubricant, however, is not needed during normal operation of the axle. This single reservoir design, in which the maximum amount of lubricant is stored in a single reservoir, is a major cause of parasitic losses, i.e., pumping losses. For example, the axle becomes less efficient due to these extra pumping losses when the axle is operating well below the maximum temperature goal in highway, cold start and short trip operating situations.
Accordingly, there is a need to increase the efficiency of vehicle axles when operating at a lower than optimal temperature.